Prior to the present invention, a wide range of plastics injection molding constructions and methods have been disclosed. U.S. Pat. No. 5,198,238, issued Mar. 30, 1993, discloses a gas assist molding device in which separable mold tooling defines a forming chamber of cavity in which a short shot of heated plastic material is injected. Subsequently, a gas injection pin inserted into the plastic material is activated so that it feeds pressurized gas into the melt to force and pack the heated plastics against the cavity wall until the material sufficiently hardens. The assist gas is subsequently discharged through the pin. U.S. Pat. No. 5,098,637, issued Mar. 24, 1992, discloses a process of injection molding a hollow plastics article with an assist gas that is introduced upon completion of plastic injection, and the gas assist is maintained for controlled purge of the plastics into a spill reservoir until the plastics solidifies. U.S. Pat. No. 4,153,231, issued May 8, 1979, discloses a mold assembly for foam molding of plastics material in which the mold forming chamber is charged with pressurized gas to suppress foaming of subsequently introduced plastics material until a skin is formed on the cavity wall surface. After such skin formation, a die is moved to an expanded position so that the material in the cavity is allowed to foam.